This invention relates to a diaphragm-controlled pressure control valve assembly, especially for fuel injection systems in internal combustion engines, in which a measuring member, disposed within a suction tube, is moved by aspirated air against a resetting force. The resetting force is supplied by a pressurized fluid, delivered through a pressure line, which continually acts upon the measuring member at a pressure which is normally constant, but which can be arbitrarily changed by means of pressure control valves.
The purpose of fuel injection systems of this kind is to create automatically a favorable fuel-air mixture for all operational conditions of the internal combustion engine so as to make possible complete combustion of the fuel and thus to avoid, or at least to sharply reduce, the production of toxic exhaust constituents while maintaining the highest possible power of the internal combustion engine or the least possible fuel consumption. Thus, the fuel quantity must be metered out very precisely according to the requirements of each operational condition of the internal combustion engine and the proportionality between the air quantity and the fuel quantity must be changed in dependence on the motor parameters such as r.p.m., load and temperature.
The change of the proportionality existing between the air quantity and the fuel quantity metered out, in dependence on engine parameters, occurs through changing the resetting force acting on the measuring member; this is done by means of pressure control valves, wherein a thin, spring-loaded steel diaphragm cooperates with a fixed valve seat. In certain pressure regions, this diaphragm spring system oscillates at its natural frequency. The oscillation not only produces an unpleasant whistle, but it also causes symptoms of wear which, in turn, result in impermissible pressure changes.